File this under things you kind of knew but now have detailed proof.

The actual halls of peak power and influence in the United States — the passageways and tunnels that lead to the U.S. Senate and its members' offices, as well as the proverbial smoke-filled rooms  where legislative deals get done — are quite literally filled with white Americans.

That's especially true if you limit your fact-finding glance to senior-level Senate staff, according to a new study released by the Joint Center for Political and Economic Studies on Tuesday.

These are the people who help members identify their legislative priorities and shape the strategy and negotiations that help a bill become law. They and an army of federal lobbyists working for industry and nonprofit groups are the people who write or edit the text of said bills, and provide the research and information that shape lawmakers' thinking. They supply the language that lawmakers use to describe their work or justify their legislative decisions in public. They also hire, manage and fire other Senate employees, staff committees and help do the backgrounding and research work that guide senators' assessment of nominees for federal jobs, judicial positions (up to and including the U.S. Supreme Court) and Cabinet secretaries who cannot be installed without Senate approval. These senior staffers are the legislative and communications directors, the chiefs of staff who really run the Senate behind the scenes.

In fact, people of color make up 36 percent of the U.S. public and 28 percent of those old enough and eligible to vote in the United States, but they are included in just 7.1 percent of all senior-level Senate staff, according to the study. And those figures are scarcely better than they were a decade ago, when people of color made up 6 percent of the entire Senate staff — prompting the magazine Diversity Inc. to publish a story about this fact under the headline, "Whose Is Worst for Diversity? The United States Senate."

Okay. Let's return to the present, shall we? You know, the time in which several large states and the nation's public schools already have minority-majority populations.

Drill down on that 7.1 percent figure and the extent of this pattern becomes clear. Of the 336 people who hold top Senate staff positions, there are only 24 people of color in this group. That's 12 Asian Americans, seven Latinos, three African Americans and two — yes two — Native Americans. Put another way, black Americans make up 13 percent of the nation's population but less than 1 percent of top Senate staff, and Latinos are 16 percent of the U.S. population but only 2.1 percent of all senior Senate staff.

Republicans long frustrated by certain allegations made against their party will love this next part: Democrats, who reliably collect large and overwhelming shares of the black, Latino, Asian and Native American votes, do not do a better job than Republicans when it comes to senior-level staff diversity. Not at all. In fact, the only black chief of staff in the entire U.S. Senate works for an African American Republican, Sen. Tim Scott from South Carolina. And, when you look at the offices of senators from states with the nation's largest minority populations, the pattern does not change.

(Click on the info graphic below to enlarge it.)

Now, there are undoubtedly many people who read the information above, who looked at the graphic and had one of two reactions. "Well, there probably aren't any qualified minorities to hold those jobs" or "Okay. So what?"

Well, The Fix is here to tell you that the first is a near mathematical impossibility. For starters, the pool of Americans with what is typically considered the base-line level of education required to hold any staff job on Capitol Hill — a bachelor's degree — is pretty diverse. There are more Asians than any other racial or ethnic group with college degrees. White Americans rank second, African Americans third.

But the biggest difference exists between Asians — 50 percent of whom have a bachelor's degree or more — and everyone else. Yet somehow, that does not hinder white worker recruitment in the Senate or many other workplaces. (Click on the chart below to enlarge it).

Those are just the facts.

Of course, that is a baseline. Some offices might also look for people with state-level lawmaking experience. But trust us, a very large share of entry-level Senate staffers have a degree and perhaps a few Hill internships on their resumes. Nothing more. Of course, to become qualified to hold a senior-level position and to guide a whole team of staffers, it's probably best to have done this work oneself. It's ideal to have first worked on a communications team, for instance, before leading one. But, if the pipelines through which people come to entry-level work, then mid- and senior-level work on the Hill aren't very big, or feed directly from a very small list of people and places (as the joint center's report also found), then the senior ranks will reflect that too. And that is a situation that has been created and fostered, not simply an inexplicable phenomenon.

As for why it matters, there is this: People who care about policy and are involved in the day-to-day work can read about the lives of other Americans, listen to constituents and go out on fact-finding missions to better understand other people's critical public policy needs. But like all human beings, senior-level Senate staffers are going to best understand and be most inclined to prioritize the issues and topics that their own experiences have made real and clear. If for no other reason than this alone, it's critical that people with a variety of experiences are working at every level and in every corner of the policy-making process.

Now, if all of that is not enough to convince you that something is amiss in the Senate staff or the staffing process that builds the Senate's staff, this might be. The reasons that the Senate staff remains so very, very white actually have a lot to do with the still-strong links between race, ethnicity and income in the United States. So, it's also very likely that white Americans who come from lower-income families, who got all of their education at public schools or who know what it's like to live on the income and benefits that come with most minimum wage jobs, are not well-represented in the senior Senate staff ranks.  Why?

The study also found that the ways by which people come to work for the Senate are incredibly insular and most readily available to a relatively select group of Americans. Yes, the jobs exist and are theoretically open to anyone who applies. But one has to know about them, know about them at the right time and get an interview. And it turns out that the people who fall in one or more of those groups often went to the same schools, churches or belong to the same families as people already working in Congress or who hold a congressional seat.

And entry-level pay in many congressional offices is so low that to take this work, it certainly helps to have little-to-no student loan debt, parents who can supplement one's income in large ways or a sufficient combination of both energy and passion for public policy to sustain a second or third job and a life in a house with several roommates. Given what we know about the disproportionate burden of student loan debt that falls on students of color and white Americans from low-income families, this alone begins to explain the trouble with senior-level Senate staff.

So, what can be done? The joint center study makes a series of recommendations. The list includes but is not limited to expanding the resources and sources that senators and their existing staff go to most often to find people to fill Senate jobs at every level, finding alternative ways such as fellowships and grants to boost pay and expand the group of Americans for whom Senate work becomes feasible. And, there's the simple but effective act of making sure that constituents and their children know that these jobs exist, that they can lead  to a career pathway and important work.

In short, those thinking of giving that job answering constituent mail to the niece of the woman who oversees communications for another senator down the hall or the son of the college roommate of a former senior press secretary, have to realize the effect. That's just not going to fix this problem.